Migrate IoT samples to Cloud Client library

Because it’s easier to instantiate client libraries, we should migrate the IoT samples to the Cloud Client library. Example code showing send command to device:

  const iot = require('@google-cloud/iot');

  const newclient = new iot.v1.DeviceManagerClient({
    // optional auth parameters.
  });

  const parentName = `projects/${projectId}/locations/${cloudRegion}`;
  const registryName = `${parentName}/registries/${registryId}`;
  const binaryData = Buffer.from(data).toString('base64');
  const request = {
    name: `${registryName}/devices/${deviceId}`,
    binaryData: binaryData,
  };
  newclient.modifyCloudToDeviceConfig(request)
    .then(responses => {
      const response = responses[0];
      // doThingsWith(response)
    })
    .catch(err => {
      console.error(err);
    });

[gguuss]

This is not fixed, will resolve once migration is complete.

[gguuss]

4/4 will wrap up when #1594 merges